Removal of hydrogen sulfide from geothermal steam

ABSTRACT

A process for removing hydrogen sulfide from saturated steam is described whereby the steam and hydrogen sulfide entrained therein are contacted under conditions of turbulent flow with hydrogen peroxide. The effectiveness of the process is improved by simultaneously contacting the steam with a basic reagent such as sodium hydroxide.

This invention relates to the removal of hydrogen sulfide from steam andto the removal of hydrogen sulfide, carbon dioxide and boric acid fromgeothermal steam before the steam is released into the atmosphere. Moreparticularly, this invention relates to a process for oxidizing hydrogensulfide entrained in geothermal steam in a simple and convenient manner.

With the decreasing availability of fossil energy sources, geothermalsteam has assumed increased importance. Exploration has opened up newfields, and known fields are being rapidly developed by drilling newwells. During the actual drilling of the well and until the well isfinished and tested, the steam is generally vented to the atmospherethrough a muffler to abate noise. After the well is brought in and theparticulate matter that is present in steam from new wells is blown off,the geothermal steam is conveyed through pipes that are usually laid onthe surface of the ground to the steam turbines of a power generatingplant.

Geothermal steam contains non-condensable gases including carbondioxide, hydrogen sulfide, hydrogen, methane, nitrogen, ammonia andboric acid. Most geothermal steam turbines are equipped with directcontact condensers which complicates environmental control because theyprovide two pathways for the effluent to return to the environment. Atthe Geysers California high pressure steam field, the steam usuallycontains between 110 and 572 parts per million (ppm) hydrogen sulfide.Pollution of the environment by hydrogen sulfide has been offensive tocommunities surrounding the polluting source because of its noxiouspresence in the atmosphere and because of its harmful effect on naturalhabitat.

Many processes have been proposed for removing hydrogen sulfide fromgaseous effluents. One of the earliest methods was the incinerationmethod. In this method, toxic hydrogen sulfide is converted to lesstoxic and less offensive sulfur dioxide and sulfur trioxide by airoxidation at high temperatures. While this process converts hydrogensulfide into sulfur dioxide, the sulfur dioxide is still noxious andpotentially dangerous to the environment.

To avoid the problems associated with the incineration method, numerouschemical processes have been suggested. U.S. Pat. No. 3,716,620discloses the oxidation of hydrogen sulfide and thiols with iodine inthe presence of an organic solvent. While this process is technicallyeffective in oxidizing hydrogen sulfide, the process is not commerciallyfeasible because the compounds used are expensive and even small lossesof these compounds make the process commercially uneconomical.

British Pat. No. 421,970 discloses a four-stage process for oxidizinghydrogen sulfide with hydrogen peroxide. In the first stage, hydrogensulfide is absorbed in an alkaline solution. In the second stage, thesolution is acidified by treatment with carbon dioxide. In the thirdstage, the solution is boiled to expel most of the absorbed hydrogensulfide. In the fourth stage, the solution is treated with an oxidizingagent to oxidize the remaining hydrogen sulfide. While the patenteestates that a tenfold reduction of hydrogen sulfide in the scrubbereffluent is achieved in fifteen minutes, this process is not acommercially feasible process, primarily because of the time necessaryto perform the complete process.

In copending U.S. application Ser. No. 472,602, filed May 23, 1974,(Belgian Pat. No. 829,372, issued Nov. 24, 1975) there is described amethod for simultaneously absorbing and oxidizing sulfur-containinggases present in a waste gas stream by contacting the waste gas streamwith aqueous hydrogen peroxide solution in a packed column such as apacked bed or tower. The waste gas stream and contacting solution may befed into the contactor either counter-currently, cross-currently orco-currently. The treated waste gas and spent aqueous hydrogen peroxidesolution are then discharged directly into the environment.

Recently, hydrogen sulfide removal from geothermal steam has beenimproved with successful testing of the Stretford process, adopted froma similar application in the coal gas industry. The Stretford processdepends on scrubbing the gas with suitable solvents, with subsequentcatalytic oxidation.

It is apparent from these prior art processes that there has been a longfelt need for a commercially effective, efficient and simple processcapable of rapidly removing hydrogen sulfide from geothermal steam in asimple and convenient manner without the formation of by-productpollutants.

In accordance with the present invention, there is provided a processfor oxidizing the hydrogen sulfide present in steam wherein the hydrogensulfide containing steam is contacted at saturation temperatures underconditions of turbulent flow with hydrogen peroxide. Surprisingly, theefficiency of this process increases markedly when the steam issaturated. Above the saturation point, it is desirable to carry out theoxidation of hydrogen sulfide present in superheated steam with hydrogenperoxide in the presence of a strong base such as an alkali metalhydroxide.

The process of this invention permits the removal of essentially all ofthe hydrogen sulfide present in geothermal steam to below levelsdetectable by conventional methods within a matter of a few seconds.Furthermore, the hydrogen sulfide is oxidized to non-polluting elementalsulfur and sulfates. These substances may be discharged directly intonatural waterways without harm to natural fauna or flora.

While the process to be described is particularly useful in thetreatment of geothermal steam, it also finds application in thetreatment of industrial waste gas streams that contain hydrogen sulfideand water vapor.

In one embodiment of the present invention, aqueous solutions ofhydrogen peroxide and a suitable base, e.g., sodium hydroxide, potassiumhydroxide, potassium carbonate or soda ash, are injected, preferably asseparate streams, directly into a steam line to abate atmosphericsulfide and any ensuring waste water sulfide. The process differs fromnormal scrubbing with caustic followed by peroxide treatment orscrubbing with a hydrogen peroxide-caustic solution, as will beexplained.

In normal scrubbing, thorough and intimate contact between a gas and arecirculating scrubbing solution occurs. This is usually carried out bycontacting a gas with a counter-current spray or series of sprays of thescrubbing solution or by using a packed bed to increase the gas toliquid contact. The scrubbing liquid is then separated from the gasstream and recirculated for additional contact.

In the present invention, the hydrogen peroxide and the base areinjected directly into the steam line, preferably in the form of aspray, although thorough gas contact with a liquid spray is notnecessary for the process to work effectively. The steam provides theunique medium whereby the sulfide reacts with the hydrogen peroxide andcaustic solutions. The small amount of the injected additives areremoved downstream with other condensates and solids and disposed of.Injecting a narrow stream rather than a spray of hydrogen peroxide andcaustic solutions is adequate and results in high abatement of hydrogensulfide. The effectiveness of the process of the present invention wasunpredictable as excessive hydrogen peroxide decomposition would beexpected to occur because of:

(1) high steam temperatures;

(2) contact with the interior of the mild steel pipe employed totransport the steam; and

(3) side reactions with other steam components such as ammonia andmethane.

The effectiveness of the process is independent of the concentration ofhydrogen sulfide present in the geothermal steam. Generally, thehydrogen sulfide gas present is source dependent and can vary from lessthan 1 ppm to as much as several thousand ppm.

It has been noted that, although the direct injection of hydrogenperoxide into the geothermal steam at a point near the well head iseffective, the reaction rate is dramatically increased when the hydrogenperoxide is injected at a point downstream where the steam has expandedand becomes saturated. The injection of a basic reagent concurrentlywith the hydrogen peroxide also increases the reaction rate and isrequired when the steam is superheated. When removing hydrogen sulfidefrom superheated steam, sufficient alkaline reagent should be injectedso that the condensate has a pH in the range of from above 7.0 to about13.5. Although a weak base such as ammonium hydroxide may be employed asthe alkaline reagent, the preferred reagent is an alkali metal hydroxidesuch as sodium hydroxide, potassium hydroxide or lithium hydroxide whichmay be replaced in whole or in part by magnesium hydroxide, calciumhydroxide, sodium carbonate, sodium bicarbonate, trona ore, potassiumcarbonate, and potassium bicarbonate.

In the practice of the present invention, any available grade of aqueoushydrogen peroxide can be employed, with a highly stabilized hydrogenperoxide being preferred. The exact quantity of hydrogen peroxideinjected into the geothermal steam depends upon the concentration of thehydrogen sulfide present in the steam and the extent to which hydrogensulfide is to be removed.

Experiments show that the percent of hydrogen sulfide abatement may becontrolled at will by adjusting the hydrogen peroxide to hydrogensulfide mole ratio and/or the sodium hydroxide to hydrogen sulfide moleratio. The molar ratio of hydrogen peroxide to hydrogen sulfide may varyfrom 0.5:1 to 30:1. Particularly preferred is a molar ratio of hydrogenperoxide to hydrogen sulfide in the range of 4:1 to 8:1. The molar ratioof base to hydrogen sulfide may vary from 0.2:1 to 30:1. The oxidationof hydrogen sulfide is particularly effective if the base is injected ata ratio of 2:1 to 8:1.

Although hydrogen peroxide is the preferred oxidizing agent, otherperoxygen compounds such as sodium carbonate peroxide, sodium perborate,sodium pyrophosphate peroxide, urea peroxide, and sodium peroxide areeffective when dissolved in water and injected into the steam. Asindicated above, the preferred alkaline reagents are the alkali metalhydroxides such as sodium hydroxide, and potassium hydroxide. Otheralkaline reagents are also effective, among them ammonium hydroxide, andsolutions of sodium carbonate, potassium carbonate, sodium bicarbonate,potassium bicarbonate, calcium hydroxide, magnesium hydroxide, sodiumperoxide and sodium carbonate peroxide.

Inasmuch as detonation may occur if hydrogen peroxide containing over 55weight percent H₂ O₂ is contacted with organic matter, desirableconcentrations of hydrogen peroxide for use in the present process areabout 35 weight percent to 50 weight percent hydrogen peroxide.

Sodium hydroxide and potassium hydroxide are commercially available as50 weight percent solutions and may be conveniently used in the processof the present invention as supplied.

The hydrogen peroxide, and the basic reagent when used, may be injectedinto the conduit at any place downstream of the well head but the tworeagents are preferably introduced in close proximity to one another toobtain the advantage provided by the turbulent flow of the steam whichmixes the reagents and assures contact with the hydrogen sulfide.Although the hydrogen peroxide and basic reagent may be mixed prior toinjection, it is desirable to introduce the two reagents separately toavoid the decomposition of hydrogen peroxide that occurs under basicconditions. Thus, the hydrogen peroxide and basic reagent may beintroduced into the conduit through separate orifices in close proximityto each other, as a spray or stream.

Although the hydrogen peroxide and alkaline reagent may be injectedintermittently, excellent mixing is obtained when the hydrogen peroxidesolution and solution of basic reagent are simultaneously injected intothe conduit carrying the steam as impinging or opposing streams orsprays co-current with the direction of steam flow or transverse to thedirection of steam flow. The alkali reagent is preferably injected at arate that maintains the pH of the geothermal steam condensate in therange of about 8 to about 13.5 and most preferably between about 8.0 andabout 11.

To reduce the hydrogen sulfide present in geothermal steam tonon-detectable limits, hydrogen peroxide may be employed inconcentrations of about 0.01% to 50% by weight. The stoichiometry of theoxidation of hydrogen sulfide by hydrogen peroxide would indicate thatfour parts by weight of hydrogen peroxide are needed to completelyoxidize one part by weight of hydrogen sulfide. However, to compensatefor decomposition losses, amounts of hydrogen peroxide slightly abovethe stoichiometric amount may be employed to oxidize all of the hydrogensulfide.

The use of hydrogen peroxide in an alkaline environment to oxidizehydrogen sulfide present in geothermal steam is completely unexpectedbecause hydrogen peroxide is known to decompose under alkalineconditions. It has been discovered, however, that the oxidiation rate ofhydrogen sulfide is significantly faster than the hydrogen peroxidedecomposition rate when hydrogen peroxide is employed in stoichiometricamounts or in amounts slightly above the stoichiometric amount.

The time necessary to completely oxidize the hydrogen sulfide ingeothermal steam with hydrogen peroxide in the presence of a basicreagent is 1-4 seconds. Conventional metal catalysts may also beemployed to assist the oxidation reaction. These catalysts include saltsof iron, cobalt, nickel, copper, manganese, molybdenum, vanadium,platinum, palladium, and silver. If a catalyst is employed, the firstfour catalytic salts are preferred. The catalyst can be employed with orwithout conventional complexing agents such as glutonic acid and citricacid, sodium tripolyphosphate, ethylene diamine tetraacetic acid and thesalts thereof. The use of a catalyst, however, is not necessary for thereaction between hydrogen sulfide and hydrogen peroxide.

The reaction temperature and pressure are critical only to the extentthat, as observed above, the hydrogen sulfide is oxidized by hydrogenperoxide much more rapidly if the steam is saturated. For this reason,in power plant operation, it is desirable to introduce the hydrogenperoxide and basic reagent downstream but close to the turbine, in theturbine chamber, or vent stack.

As indicated above, when bringing in a new well, the geothermal steam isnormally vented to the atmosphere through a muffler to reduce the noise.Under these circumstances, injection of hydrogen peroxide and analkaline reagent into the blooie line upstream of the muffler willoxidize the hydrogen sulfide. The quantity of hydrogen peroxide andbasic reagent injected into the blooie line may be controlled withpositive displacement pumps and monitored by analyzing the condensatefrom the muffler for alkali and residual hydrogen peroxide. Commerciallyavailable gas analyzers may be used to analyze the hydrogen sulfide gascontent of the vented steam.

In employing the process of the present invention to control thehydrogen sulfide emissions from a commercial steam generating plant, thehydrogen peroxide and alkaline reagent are injected into the steamupstream or downstream of the turbine or directly into the turbinechamber. Again the precise amount of reagents injected to obtain thedesired degree of hydrogen sulfide abatement may be controlled bycontinuous or intermittent analysis of the vented steam and condensatefor hydrogen sulfide, hydrogen peroxide and alkalinity.

When geothermal steam is used to power a generating plant, the wells arenot shut down during maintenance work on the plant or turbines, as anyinterruption of steam flow would result in the accumulation of solidsand serious abrasion of the turbines for an appreciable time after thewells are brought back into operation. Accordingly, the geothermal steamis bypassed during maintenance on the generating plant and venteddirectly to the atmosphere through large mufflers. The process of thepresent invention is extremely effective in preventing pollution of theatmosphere with hydrogen sulfide during such periods of plantmaintenance or shut down. The hydrogen peroxide alone, or hydrogenperoxide and alkaline reagent are injected into the steam at theentrance to the muffler.

One surprising aspect of the inventive process is the fact that a strongalkali such as sodium hydroxide is more effective in reducing thehydrogen sulfide content of geothermal steam than a weaker basic reagentsuch as ammonium hydroxide. This was completely unexpected as severalfactors were believed to mitigate against the successful operation ofsuch systems; namely:

(1) high peroxide decomposition losses due to high pH of the causticsolution present;

(2) the rapid migration of sodium hydroxide to the walls of the mildsteel steam pipe, severely reducing contact of the caustic with thehydrogen sulfide gas. The sodium hydroxide not being volatile wasexpected to rapidly become ineffective after entering the steam line.

The use of hydrogen peroxide alone in the absence of an alkaline reagentresults in corrosion of mild steel which corrosion is reduced by theaddition of an alkaline reagent intermittently or simultaneously withthe hydrogen peroxide.

The following examples further illustrate the invention. All percentagesgiven are based upon weight unless otherwise indicated.

EXAMPLE I

Hydrogen sulfide is oxidized at pH 7-8 with hydrogen peroxide by passingdilute solutions of hydrogen sulfide and hydrogen peroxide through avaporizer into a glass reaction tube two feet in length and one inch indiameter.

The hydrogen sulfide solutions are prepared by bubbling hydrogen sulfidegas through water to produce separate solutions, each containing 12.5ppm and 27.1 ppm of hydrogen sulfide and adjusting the pH to 7-8 withdilute ammonium hydroxide. The hydrogen peroxide solutions are preparedby diluting 35% by weight hydrogen peroxide with dionized water toprovide solutions containing 48 and 90 ppm separately of hydrogenperoxide. The two foot reaction tube terminates in a glass flasksurrounded by dry ice to condense the steam and stop the oxidationreaction.

To test the effect of mild steel on the decomposition of hydrogenperoxide, a mild steel pipe was inserted into the glass reaction tubefor selected experiments. Flow rates of the hydrogen peroxide andhydrogen sulfide solutions are adjusted to simulate the 3-4 secondresidence time that is found in actual geothermal field situations. Thesulfide content is determined on the condensate immediately after eachrun using a methylene blue test kit. Hydrogen peroxide assays arecarried out using a spectrophotometer with o-toluidine reagent.

The results are summarized in Table I, and show that in the absence ofmild steel, a substantial quantity of hydrogen peroxide remains stablewithin the 3-4 second reaction time. (Table I, Runs A-B). Mild steel,however, results in high hydrogen peroxide decomposition losses (TableI, Runs C-I).

A significant improvement in the hydrogen sulfide abatement results whenthe temperature of steam is lowered to the saturation temperature of100° C. at 760 millimeters Hg (Table I, Run E).

The temperature in geothermal steam line cannot always be convenientlycontrolled, but it is apparent from Table I

                                      TABLE I                                     __________________________________________________________________________                      Average                                                                              Residence                                            Run                                                                              mg/l                                                                              H.sub.2 S                                                                          Mole Ratio                                                                          Temperature                                                                          Time  % H.sub.2 O.sub.2                                                                     % H.sub.2 S                                                                          Reactor Tube                    No.                                                                              H.sub.2 O.sub.2                                                                   Charged                                                                            H.sub.2 O.sub.2 /H.sub.2 S                                                          °C.                                                                           Seconds                                                                             Decomposition                                                                         Abatement*                                                                           Construction                    __________________________________________________________________________    A  48  --     1/0 146    3-4   24      --     glass                           B  48  12.5 3.8/1 146    3-4   24        26.4 glass                           C  48  --     1/0 122    3-4   96      --     glass-mild steel                D  48  12.5 3.8/1 156    3-4   97      20     glass-mild steel                E  48  12.5 3.8/1 100    3-4   98      82     glass-mild steel                F  48  12.5 3.8/1 195    3-4   100      0     glass-mild steel                G  48  12.5 3.8/1 128    3-4     99.6  32     glass-mild steel                H  --  12.5   0/1 128    3-4   --       0     glass-mild steel                I  90  27.1 3.3/1 165    3-4     99.6  44     glass-mild                      __________________________________________________________________________                                                  steel                            *Adjusted to pH 7-8 with NH.sub.4 OH                                     

that injection of hydrogen peroxide into steam at the saturation pointwill enhance the hydrogen sulfide abatement.

EXAMPLE II

A one liter Erlenmeyer flask containing 500 ml of a 0.283 weight percentsodium sulfide solution adjusted to pH 7 is covered loosely with a pieceof aluminum foil to permit steam to escape from the flask whilepreventing spray from entering the flask. An 18 inch long, 2 inch IDdiameter heated glass tube is placed over the flask in a verticalposition and the hydrogen sulfide solution is heated to the boilingpoint.

A spray of dilute hydrogen peroxide is directed downward from a positionapproximately 1 inch above the top of the vertical tube. The degree ofhydrogen sulfide abatement is established by placing Drager tubes overthe steam vent before and during the spraying operations.

Excellent abatement of the hydrogen sulfide with hydrogen peroxide isachieved by this spraying technique in those experiments summarized inTable II.

                  TABLE II                                                        ______________________________________                                        Effect of Spraying Dilute H.sub.2 O.sub.2 Solution Into                       Rising Steam Vapors Containing H.sub.2 S                                                                       %*                                                                            Atmospheric                                  Run     H.sub.2 S                                                                            H.sub.2 O.sub.2                                                                         Mole Ratio                                                                            H.sub.2 S                                    No.     mg/l   mg/l      H.sub.2 O.sub.2 /H.sub.2 S                                                            Abatement                                    ______________________________________                                        1-A     79     477       6/1     80.8                                         2-A     79     477       6/1     52.5                                         3-A     79     477       6/1     93.3                                         ______________________________________                                         *By Drager Test                                                          

This example establishes that hydrogen sulfide may be removed fromgeothermal steam by directing a hydrogen peroxide spray upward ordownward into a drilling muffler or into a power plant vent stack wherethe condition of steam saturation is satisfied.

EXAMPLE III

The use of hydrogen peroxide in removing hydrogen sulfide fromgeothermal steam was evaluated in a field trial on a pilot plant scale.Two and three-tenths inch ID mild steel, Schedule 40 piping is used forthe muffler blooie line construction except for a three foot section oftype 316 stainless steel pipe. This stainless steel pipe is placed atthe chemical injection point to minimize iron catalyzed peroxidedecomposition. Mixing of the chemical spray with the steam was improvedwith a venturi possessing a 0.30 inch throat installed a few feetdownstream from the chemical injection point. The steam flow is measuredby a Barton differential flowmeter. The hydrogen peroxide and alkalisolutions are metered by positive displacement pumps. Spray headspositioned within the stainless steel section of the pipe deliver astream or spray (depending on the flow rate) of hydrogen peroxide orhydrogen peroxide and alkali reagent solutions. In the preferredconfiguration, the spray head is directed downstream parallel to thesteam flow.

Atmospheric hydrogen sulfide is routinely determined at the muffleroutlet by drawing steam vapor through a Drager tube for 15 seconds.Sulfides in the muffler condensate are determined with a Lamott-PomeroyModel CC PS 4630 kit based on methylene blue development. The totalhydrogen sulfide in the steam is determined by condensing a side streamof the steam. In order to condense the side stream, a slight backpressure is needed. This is achieved

                                      TABLE III                                   __________________________________________________________________________    Field Trial on H.sub.2 S Abatement in Geothermal Steam                                                               Solu-                                                                         tion   Temp. °F.                                                                      Atmos-                                                         Feed                                                                             Steam                                                                             At      pheric                                                                            Solution                                                   Rate                                                                             Flow                                                                              Chemical                                                                           At H.sub.2 S                                                                         Injection           Run                                                                              Wt. %            Mole Ratios        ml/                                                                              Rate                                                                              Injection                                                                          Muf-                                                                             Abate-                                                                            Charac-             No.                                                                              H.sub.2 O.sub.2                                                                   NH.sub.4 OH                                                                        NaOH                                                                              Water                                                                             H.sub.2 O.sub.2 /H.sub.2 S                                                          NH.sub.4 OH/H.sub.2 S                                                                NaOH/H.sub.2 S                                                                      min.                                                                             lbs./hr.                                                                          Point                                                                              fler                                                                             ment*                                                                             teristic            __________________________________________________________________________     1 1.37                                                                              --   --  98.63                                                                             4/1   --     --     99                                                                              117 251  206                                                                               7  spray                3 4.80                                                                              --   --  95.20                                                                             15.3/1                                                                              --     --    109                                                                              119 251  193                                                                              33  spray                4 4.80                                                                              --   --  95.20                                                                             19/1  --     --    110                                                                               96 251  192                                                                              37  spray               13 35.0                                                                              --   --  65  136/1 --     --    100                                                                              102 256  192                                                                              56  drip                14 35.0                                                                              --   --  65  225/1 --     --    168                                                                              102 256  192                                                                              64  stream              15 35.0                                                                              --   --  65  285/1 --     --    215                                                                              102 256  192                                                                              78  spray                6 4.8 0.25 --  94.95                                                                             19.8/1                                                                              1.2/1  --    110                                                                               92 250  193                                                                              46  spray                5 4.8 0.50 --  94.70                                                                             19.1/1                                                                              1.9/1  --    110                                                                               96 251  193                                                                              36  spray                7 4.8  0.125                                                                             --  95.07                                                                             19.8/1                                                                              0.6/1  --    110                                                                               92 254  184                                                                              68  spray               12 0    0.125                                                                             --  99.88                                                                             --    0.6/1  --    125                                                                               93 252  192                                                                              15  stream              19 0.6 --   0.5     1.9/1 --     1.3/1  83                                                                               93 253  191                                                                              63  drip                20 0.89                                                                              --   0.47    2.7/1 --     1.2/1  83                                                                               93 252  183                                                                              73  drip                24 1.2 --   0.24    3.1/1 --     0.5/1  83                                                                               93 255  192                                                                              58  drip                25 1.2 --   0.95    3.8/1 --     2.6/1 102                                                                              110 252  193                                                                              88  drip                18 1.2 --   0.48    5.6/1 --     1.9/1 125                                                                               93 253  191                                                                              84  stream              30 1.2 --   0.95    6.7/1 --     3.8/1 144                                                                              110 253  193                                                                              96  stream              31 1.2 --   0.95    8/1   --     4.6/1 213                                                                              110 253  193                                                                              96  spray               27 1.2 --   0.95    4/1   --     2.3/1 112                                                                              110 254  193                                                                              91  drip                29 1.2 --   0.95    7.8/1 --     4.4/1 207                                                                              110 254  193                                                                              93  spray               22 --  --   1.4     --    --     3.1/1  83                                                                              102 249  189                                                                              66  drip                17 --  --   0.48    --    --     1.8/1 125                                                                               93 256  192                                                                              58  steam               __________________________________________________________________________     *By Drager measurements                                                  

by welding a metal plate with an 0.5 inch opening on top of the 8 inchmuffler opening. The side stream enters a solution of soluble cadmiumsalt to form insoluble cadmium sulfide. This precipitate is analyzed andcalculated back to hydrogen sulfide. The data obtained is summarized inTable III.

Run No. 27 is indicative of the results obtained with the process of thepresent invention. The sulfide abatement of 91% is achieved using a2.3:1 mole ratio of sodium hydroxide to sulfide and a 4:1 ratio ofhydrogen peroxide to sulfide.

The analysis of the condensate from Run 31 above appears in thefollowing Table IV.

                  TABLE IV                                                        ______________________________________                                        Analyses of Condensate From Run 31                                                               Wt. %                                                                         (of sulfur con-                                                        mg/l   taining species)                                           ______________________________________                                        Free Sulfur   0.4      0.01                                                   Sulfide       0.3      0.009                                                  Sulfite       0.8      0.03                                                   Thiosulfate   368      11.8                                                   Sulfate       2731     88.1                                                   Carbonate     4250                                                            ______________________________________                                    

What is claimed is:
 1. A process for removing hydrogen sulfide fromgeothermal steam which comprises passing geothermal steam containinghydrogen sulfide through a steam pipe at a temperature below 195° C.,but not below the boiling point of water at atmospheric pressure, underconditions of turbulent flow and injecting into said steam pipe a baseand hydrogen peroxide.
 2. The process of claim 1 wherein the basicreagent and hydrogen peroxide are injected as impinging liquid streams.3. The process of claim 1 wherein the basic reagent and hydrogenperoxide are sprayed into said conduit.
 4. The process of claim 1wherein the hydrogen peroxide is injected as a 50 weight percentsolution.
 5. The process of claim 1 wherein said base is aqueousammonium hydroxide.
 6. The process of claim 1 wherein said steam issuperheated.
 7. The process of claim 1 wherein said steam is saturated.8. The process of claim 1 wherein the mole ratio of hydrogen peroxide tohydrogen sulfide is in the range of from about 4:1 to about 8:1.
 9. Aprocess for removing hydrogen sulfide from geothermal steam whichcomprises passing geothermal steam containing hydrogen sulfide through asteam pipe at a temperature below 195° C., but not below the boilingpoint of water at atmospheric pressure, under conditions of turbulentflow and simultaneously injecting into said steam pipe a base andhydrogen peroxide.
 10. A process for removing hydrogen sulfide fromgeothermal steam which comprises passing geothermal steam containinghydrogen sulfide through a confined area within a steam pipe at atemperature below 195° C., but not below the boiling point of water atatmospheric pressure, under conditions of turbulent flow and injectingupstream of said confined area a base and hydrogen peroxide.
 11. Aprocess for removing hydrogen sulfide from geothermal steam whichcomprises passing geothermal steam containing hydrogen sulfide at atemperature below 195° C. but not below the boiling point of water atatmospheric pressure through a conduit and injecting into said conduitan alkaline acting reagent and an inorganic peroxygen compound.
 12. Aprocess for removing hydrogen sulfide from geothermal steam whichcomprises passing geothermal steam containing hydrogen sulfide through aconduit and introducing into said conduit an alkaline acting reagent andan inorganic oxidizing agent under conditions sufficient to effect areduction in the hydrogen sulfide content of said steam.
 13. A processfor removing hydrogen sulfide from geothermal steam which comprisespassing geothermal steam containing hydrogen sulfide through a conduitand introducing into said conduit an alkaline acting reagent and aninorganic peroxygen oxidizing agent under conditions sufficient toeffect a reduction in the hydrogen sulfide content of said steam.
 14. Inthe process of removing hydrogen sulfide from geothermal steam employedas an energy source to drive a turbine, and vented to the atmosphere,the improvement which comprises removing a substantial portion of thehydrogen sulfide present in the steam by contacting the steam at atemperature below 195° C., but not below the boiling point of water atatmospheric pressure, under conditions of turbulent flow with hydrogenperoxide and a base.
 15. A process for removing hydrogen sulfide fromgeothermal steam which comprises passing geothermal steam containinghydrogen sulfide at a temperature below 195° C., but not below theboiling point of water at atmospheric pressure, through a steam pipeunder conditions of turbulent flow and injecting into said steam pipe abase and an inorganic peroxygen compound.